netdev - Re: [PATCH] IP: Increment INADDRERRORS if routing for a packet is not successful

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Date:	Wed, 2 Jun 2010 10:27:13 -0500 (CDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	netdev@...r.kernel.org, Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] IP: Increment INADDRERRORS if routing for a packet is
 not successful

On Wed, 2 Jun 2010, Eric Dumazet wrote:

> Le mardi 01 juin 2010 à 16:13 -0500, Christoph Lameter a écrit :
> > Something like this would have been very helpful during recent debugging
> > of multicast issues. Silent discards are bad.
> >
>
> >
> > If the kernel perceives that something is wrong with an incoming packet then the
> > IP stack currently silently discards packets. This makes it difficult to diagnose
> > problems with the network configurations (such as a misbehaving kernel
> > subsystem discarding multicast packets because the reverse path filter
> > does not like multicast subscriptions on the second NIC with rp_filter=1).
> >
> > It is also necessary to know how many inbound packets are discarded to
> > assess networking issues in general with a NIC.
> >
> > Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>
> > Acked-by: Stephen Hemminger <shemminger@...tta.com>
> >
>
> I disagree with this patch.
>
> IPSTATS_MIB_INADDRERRORS has a strong meaning, part of RFCS.
>
> In this path, we simulate the routing of a virtual packet, not its
> delivery.
>
> This should not affect IPSTATS SNMP entries.
>
> You should use another MIB entry, say LINUX_MIB_INROUTEERRORS ?
>
> Dont inet_rtm_getroute() caller gets an error status anyway ?

Yes but they are not increment any counter. If packets are dropped because
of the rp_filter setting interfering f.e. then the packets vanish without
any accounting.

LINUX_MIB_INROUTEERRORS? Does it mean I can create a series of new
counters that allow us to diagnose and distinguish all the different
causes of packet loss? We would love to have that.